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Nigel
The Cast Ali throttle cross tube triangular Support posts on your AC Aceca ( and Ace) LHD & RHD are the same as those used on the 2 litre saloon. and are
also used on the Bristol engine Ace & Aceca LHD & RHD.
As stated in earlier post David Whitehouse had some cast, just leaves you to make up cross shaft and linkage to the SU carbs, which I believe David Whitehouse could well have the parts you require,
Re: James observation.
Irrespective of location close to or further away from the bulkhead, Ali foot box in Ace or Glass fibre in the Aceca, the support posts appear the identical.
Obviously the linkage varies LHD to RHD and AC or Bristol engine.
Keith